A pressure sensor comprises a micromechanical sensor element and an evaluation circuit, which are arranged in a common housing. The housing protects the individual components against environmental influences, such as dust, vibration and heat, and therefore the pressure sensor can be used, for example, on board a motor vehicle. The micromechanical sensor element comprises a membrane, the deformation or deflection of which because of atmospheric pressure is converted into a sensor signal which is then further processed by means of the evaluation Circuit. A plurality of techniques are known for accommodating the sensor element and the evaluation circuit in a housing.
In a first variant, a housing part produced by casting is produced with a depression in which the sensor element and the evaluation circuit are subsequently attached. Electric contacts between said elements then still have to be passivated, which can be complicated and cost-intensive.
In a second variant, the evaluation circuit and optionally other passive components are arranged on a substrate and encapsulated by moulding. A depression in which the micromechanical sensor element is attached in a second placement process is produced at the same time during the casting. However, electric contacts then have to be passivated again, and therefore the process flow comprises two sequential placements. On the other hand, it is advantageous here that, except for the micromechanical sensor, all of the components are enclosed in the potting compound and are therefore readily protected against environmental influences. The potting compound can provide better protection than a subsequently applied passivation material, such as, for example, a silicone gel.
In a third variant, the sensor element is placed together with the evaluation circuit on the substrate and made contact with before the pressure sensor is potted with a potting compound. For this purpose, a film customarily has to be inserted between a potting die and the substrate in order to ensure tightness in relation to the potting compound. As a result, one placement process is sufficient, and the sensor element remains accessible from the outside even in the finished state of the sensor. It is disadvantageous in this connection that the potting die has to be sealed off from the membrane of the sensor element. In the process, the membrane may easily be damaged or the tightness in relation to the potting compound cannot be ensured. Overflowing potting compound (mould) can soil individual components, such as the pressure sensor and, in particular, the membrane thereof (mould flash). If the membrane comes into contact with potting compound, the sensor signal may be falsified as a result.